. >> president obama opens his agrees to the u.n. with a tribute to the late u.s. ambassador to libya and bay area native, chris stevens. i'm kristen sze. >>> and i'm cheryl jennings. >> he called attacks that killed the ambassador and three others assault on the ideals on which the u.s. was founded and issued a strong warning to iran. >> reporter: the backdrop for the president's address to the united nations this morning was a flexing of military muscle in the persian gulf. -- gulf the president paid tribute to the four americans killed during the attacks in libya. >> the president: we must reaffirm our future will be determined by people like chris stevens not by his killers. today we must declare this violence and intolerance has no place among our united nations. >> reporter: the remarks at the u.n. this morning sent an unmistakeable message. >> the president: make no mistake a nuclear armed iran is not a challenge that can be contained. it would threaten the elimination of israel and the stability of the global economy. >> reporter: israel has threatened a ai